1. Field of the Invention
The present invention relates to a method for forming an interlayer dielectric film, an interlayer dielectric film, a semiconductor device, and a semiconductor manufacturing apparatus; and particularly to a method for forming an interlayer dielectric film in which change over time is reduced, and an interlayer dielectric film formed by the method.
2. Description of the Related Art
Conventionally, silica (SiO2) has been widely used as an interlayer dielectric material for use in the copper wiring layer of semiconductor devices. As semiconductor devices have become miniaturized and increased in speed, however, films with lower dielectric constants have increasingly been used as interlayer dielectric films, in order to reduce signal transmission delays in the wiring and the power consumption. Pores or hydrocarbons are typically introduced to reduce the dielectric constant, and methods such as a plasma CVD method and spin coating are used to produce interlayer dielectric films. Some interlayer dielectric films obtained using these methods are reported to have dielectric constants of 2.4 or less; however, due to reduced mechanical strength caused by an increase in pores or hydrocarbons, the interlayer dielectric films have the problem of lowered reliability due to removal during the semiconductor process.
For this reason, considering the mechanical strength, the plasma CVD method is often employed to form interlayer dielectric films. In most cases of growing interlayer dielectric films using the plasma CVD method, a carrier gas of an inert gas, as well as a mixed gas of a raw-material organic silane gas and an oxidizing gas are introduced into a reactor, and an oxidization reaction of the raw-material gas with the oxidizing gas is promoted in a plasma to grow an interlayer dielectric film.
An increase in pores or hydrocarbons causes not only lowered mechanical strength but also the adsorption of moisture in the atmosphere. The moisture adsorption in the pores raises a concern for an increase in the dielectric constant. In addition, the adsorbed moisture causes the decomposition of hydrocarbons, which is one cause of an increased dielectric constant. In particular, when a film is formed by the plasma CVD method, decomposition products of raw materials due to plasma reactions are not terminated, possibly resulting in sites where moisture is adsorbed. Interlayer dielectric films containing fluorine, in particular, have significantly increased dielectric constants due to moisture absorption. For this reason, Japanese Patent Laid-Open No. 11-330070 introduces an approach of introducing hydrogen during film formation to obtain a stable film, Japanese Patent Laid-Open No. 2006-253290, on the other hand, describes a method for removing reaction products by purging with an inert gas prior to film formation.
Using the technique described in Japanese Patent Laid-Open No. 11-330070, however, the formation of a film using a hydrogen reaction is difficult to control because the system is complicated due to the introduction of two types of gases, and the reduction of the film itself is induced. Moreover, even if purging with an inert gas is performed prior to film formation, as described in Japanese Patent Laid-Open No. 2006-253290, it is impossible to remove the reaction products formed during the subsequent formation of an interlayer dielectric film, consequently causing the dielectric constant of the film to change over time. Such a change over time in the dielectric constant of a film is apparent in the plasma polymerization method or plasma copolymerization method. The plasma polymerization method is a general term for one embodiment of the plasma CVD method, in which a mixed gas of an inert gas and a monomer with an unsaturated hydrocarbon is activated in a plasma without using an oxidizing gas, thereby growing an interlayer dielectric film having the monomer as a portion of its skeleton. The plasma copolymerization method is a method in which an interlayer dielectric film is grown using a plurality of raw-material monomers and an inert gas without the addition of an oxidizing gas. To form interlayer dielectric films using these plasma reactions, a method is required that is simple and reduces change over time in the dielectric constant. The present invention has been made in view of the above-described circumstances, and aims to provide an interlayer dielectric film in which change over time is reduced and which is stable for a long period, a semiconductor device using the interlayer dielectric film, and a method for manufacturing the semiconductor device.